1. Field of the Invention
The present invention concerns wireless communications, and more specifically, to a method of monitoring a control channel in a wireless communication system and a wireless device using the same.
2. Related Art
3GPP (3rd Generation Partnership Project) TS (Technical Specification) Release 8-based LTE (Long Term Evolution) is the potent next-generation mobile communication standard. Recently, LTA-A (LTE-Advanced) based on 3GPP TS release 10 supporting multiple carriers are underway for its standardization.
Mobile communication systems are also adopting MIMO (Multiple Input Multiple Output) technique using multiple antennas. 3GPP LTE supports up to four transmission antennas and 3GPP LTE-A supports up to eight transmission antennas.
The MIMO technology comprises a spatial diversity scheme in which data symbols are transmitted via various pathways to thereby increase transmission reliability and a spatial multiplexing scheme in which multiple data symbols are simultaneously transmitted through multiple transmission antennas. Further, MIMO schemes may be separated into SU-MIMO (Single User-MIMO) and MU-MIMO (Multi User-MIMO).
The capacity of a MIMO channel increases in proportion to the number of antennas. A MIMO channel may be split into independent channels. Assuming that the number of transmission antennas is Nt and the number of reception antennas is Nr, the number of independent channels, Ni, meets Ni≦min{Nt, Nr}. Each independent channel may correspond to a layer. The layer may be defined as an information path that is input to a precoder. The rank is the number of non-zero eigen values in a MIMO channel matrix and is equal to the number of layers or the number of space streams.
In 3GPP/LTE-A, the control channel does not support multi-antenna transmission. The control channel has been designed to assume transmission through a single antenna.
However, to respond to increasing control information and to increase scheduling flexibility, control channels need to be transmitted via multiple antennas, and a need exists for monitoring the same.